Histamine Effects on Blood Vessels and Immunity: L18-19
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Questions and Answers

What effect does histamine have on blood vessels?

  • Increased vascular permeability (correct)
  • Decreased blood flow to tissues
  • Constriction of arterioles
  • Smooth muscle relaxation
  • Which immune components are mentioned as being influenced by the H4 receptor?

  • Thyroid and adrenal glands
  • Platelets and red blood cells
  • Spleen, thymus, and leukocytes (correct)
  • Bone marrow and lymph nodes
  • What condition may benefit from research into the H4 receptor?

  • Hypertension
  • Rheumatoid arthritis (correct)
  • Asthma
  • Diabetes
  • What is one of the primary actions of histamine (H1) on smooth muscle?

    <p>Contraction of bronchial smooth muscle</p> Signup and view all the answers

    Which symptom is most directly associated with the stimulation of peripheral nerves by histamine?

    <p>Pain and itch</p> Signup and view all the answers

    Which of the following is NOT an action of histamine (H1)?

    <p>Reduction of vascular permeability</p> Signup and view all the answers

    What happens in the body as a result of histamine causing vasodilation?

    <p>Increased heat and redness</p> Signup and view all the answers

    Which option best describes allergy in relation to histamine?

    <p>A sensitivity to specific allergens</p> Signup and view all the answers

    What is one of the primary effects of histamine on smooth muscle in the context of asthma?

    <p>Contraction of bronchial passages</p> Signup and view all the answers

    Which action of histamine contributes to the sensation of pain or itch?

    <p>Stimulation of peripheral nerves</p> Signup and view all the answers

    What occurs during the administration of small doses of histamine to the cardiovascular system?

    <p>Drop in blood pressure</p> Signup and view all the answers

    What is the potential consequence of large doses of histamine on the cardiovascular system?

    <p>Anaphylactic shock</p> Signup and view all the answers

    What effect does histamine have on the arterioles in the cardiovascular system?

    <p>Dilates arterioles</p> Signup and view all the answers

    What side effects are associated with H1 receptor antagonists like mepyramine?

    <p>Drowsiness</p> Signup and view all the answers

    What physiological response leads to the wheal-and-flare reaction when histamine is injected?

    <p>Neuronal stimulation and local vasodilation</p> Signup and view all the answers

    Which statement accurately describes the action of histamine on veins?

    <p>Veins are constricted, increasing pressure in venules</p> Signup and view all the answers

    Which of the following is a classical H2 receptor antagonist?

    <p>Cimetidine</p> Signup and view all the answers

    What is a noted action of the H2 receptors in the immune system?

    <p>Inhibiting histamine release from mast cells</p> Signup and view all the answers

    Which condition is NOT a use for H2 receptor antagonists?

    <p>Hypertension</p> Signup and view all the answers

    What unique characteristic is noted about histamine release in the CNS?

    <p>It follows a distinct circadian pattern</p> Signup and view all the answers

    What is a potential use of H3 receptor antagonists, as mentioned?

    <p>Controlling sleep/wake cycles</p> Signup and view all the answers

    Where are H4 receptors primarily identified?

    <p>Inflammatory cells</p> Signup and view all the answers

    Which statement about histamine in pregnancy is accurate?

    <p>It contributes to embryo-uterine interactions</p> Signup and view all the answers

    What effect does cimetidine have on drug metabolism?

    <p>It inhibits cytochrome P450, retarding drug metabolism</p> Signup and view all the answers

    What is the primary amino acid precursor for the synthesis of histamine?

    <p>Histidine</p> Signup and view all the answers

    Where in the body is histamine primarily stored?

    <p>Mast cells</p> Signup and view all the answers

    What pH value corresponds to histamine being normally uncharged?

    <p>pH 5.74</p> Signup and view all the answers

    Which type of receptor does histamine NOT have?

    <p>H5</p> Signup and view all the answers

    What is a characteristic of dietary histamine?

    <p>It does not contribute to the body's pool of histamine.</p> Signup and view all the answers

    Which condition is associated with excessive histamine release?

    <p>Allergy</p> Signup and view all the answers

    What is the primary role of histamine in the body?

    <p>Acting as a local hormone or autacoid</p> Signup and view all the answers

    What is a common source of histidine in the diet?

    <p>Red meat</p> Signup and view all the answers

    Which statement about mast cells is accurate?

    <p>They can contain 3-4 picograms of histamine per granule.</p> Signup and view all the answers

    What pharmacological use of antihistamines is most recognized?

    <p>To reduce allergic symptoms</p> Signup and view all the answers

    What effect does the activation of 5-HT1 receptors have on the body?

    <p>Neural inhibition and vasoconstriction</p> Signup and view all the answers

    Which drug is an effective 5-HT1D agonist used for treating migraines?

    <p>Sumatriptan</p> Signup and view all the answers

    What is the primary effect of LSD on 5-HT2 receptors in the central nervous system?

    <p>It acts as an agonist to increase neuron inhibition</p> Signup and view all the answers

    Which of the following statements is true regarding 5-HT3 receptors?

    <p>They are involved in evoking pain mainly in the peripheral nervous system.</p> Signup and view all the answers

    Which of the following is a recognized use of 5-HT3 receptor antagonists like ondansetron?

    <p>To control severe vomiting and nausea from cancer chemotherapy</p> Signup and view all the answers

    Which receptor class does LSD act as an antagonist on in the periphery?

    <p>5-HT2 receptors</p> Signup and view all the answers

    Which of the following drugs was previously used to treat migraines before the invention of triptans?

    <p>Methiothepin</p> Signup and view all the answers

    What is the main physiological role of 5-HT4 receptors?

    <p>Influencing gastrointestinal motility</p> Signup and view all the answers

    What is the primary role of 5-HT4 receptor agonists like tegaserod in gastrointestinal conditions?

    <p>To alleviate abdominal discomfort and constipation</p> Signup and view all the answers

    In which way does 5-HT contribute to gastrointestinal motility?

    <p>By stimulating GI motility via multiple receptor pathways</p> Signup and view all the answers

    What effect does 5-HT have on blood pressure following its injection?

    <p>Leads to an initial rise in blood pressure followed by a decline</p> Signup and view all the answers

    How does 5-HT affect platelets during the clotting process?

    <p>It promotes platelet stickiness and hemostasis</p> Signup and view all the answers

    What is one indirect effect of 5-HT on the cardiovascular system?

    <p>Triggers nitric oxide release from endothelial cells</p> Signup and view all the answers

    How does 5-HT influence venous blood flow?

    <p>By constricting veins and pooling blood in capillaries</p> Signup and view all the answers

    What is the relationship between 5-HT and migraine according to the content?

    <p>It is believed to have a role in migraine pathophysiology</p> Signup and view all the answers

    Which receptor type is primarily stimulated by 5-HT in the gut to facilitate fluid secretion and nausea?

    <p>5-HT3 receptors</p> Signup and view all the answers

    Study Notes

    Histamine and 5-HT

    • Histamine and 5-HT are biogenic amines, small molecules (approximately 100 molecular weight). They act as local hormones or autacoids. They're important neurotransmitters in the vasculature and smooth muscle.

    Histamine

    • Structure: Histamine has an imidazole ring and an amino group. The imidazole ring has a pKa of 5.74, while the amino group has a pKa of 9.8.
    • Synthesis and metabolism: Histamine is synthesized from histidine by histidine decarboxylase. The body can metabolize histamine, with pathways including N-methylation and diamine oxidase.
    • Storage and release: Histamine is stored in mast cells, which are long-lived tissue resident cells containing up to 1,000 granules (3-4 pg per cell). Different tissues (lung, skin, gut, stomach) have variable histamine concentrations. Release is triggered in different ways. Mast cells have IgE receptors enabling IgE-dependent release. Other stimuli like bacterial products (LPS) and complement peptides (C3a and C5a) also activate mast cells via specific receptors, leading to histamine release. Non-receptor actions by other substances, like basic drugs and trauma, can also trigger histamine release.
    • Histamine receptors: There are four main histamine receptors (H1, H2, H3, H4). Each receptor subtype has a unique location and function in the body.
    • Antihistamine drugs: Drugs that block histamine receptors are used to treat various conditions like allergies and motion sickness. Examples include mepyramine and cetirizine (for H1 receptors) and cimetidine (for H2 receptors).

    Histamine and Human Diseases

    • Peptic ulcer refers to breaks in the stomach lining, first part of the small intestine, or sometimes the lower esophagus.
    • Allergy is a sensitivity to a specific substance (allergen). Contact through skin, inhalation, or injection may trigger an allergic response.

    Histamine Receptors (H1)

    • Location: Widely distributed in the cardiovascular system, smooth muscle, and peripheral nerves.
    • Effect: Vasodilation, increased vascular permeability, stimulation of peripheral nerves, smooth muscle contraction. This leads to conditions such as redness, heat, swelling, pain and itching (e.g., in allergic reactions).

    Histamine Receptors (H2)

    • Location: Specific locations, mainly in gastric parietal cells, and vascular smooth muscle, neutrophils, CNS, heart and uterus.
    • Effect: Stimulates gastric acid secretion. Regulates cardiac output and rate. Modulates immune cell actions.

    Histamine Receptors (H3)

    • Location: Primarily found in the CNS, with high concentrations in the thalamus, caudate nucleus, and cortex. Lower levels detected in the small intestine, testes, and prostate.
    • Effect: Histamine plays a role as a neurotransmitter. Release follows a distinct circadian pattern occurring during the day but not at night.

    Histamine Receptors (H4)

    • Location: Widely expressed in components of the immune system (spleen, thymus, leukocytes).
    • Effect: Unknown, but potentially involved in regulating cytokine networks within the inflammatory response

    5-Hydroxytryptamine (5-HT) / Serotonin

    • Location: Found in the CNS, gastrointestinal tract, and platelets.
    • Function: Important neurotransmitter, playing key roles in the gastrointestinal tract and vascular system. Various functions related to mood, behaviour, thermoregulation, appetite regulation and sleep.
    • Human Diseases: Migraines, depression.
    • Levels of 5-HT and symptoms: Too much or too little 5-HT is associated with certain conditions (e.g., cardiac valve pathology, serotonin syndrome, depression, anxiety, OCD).
    • Structure: Contains a hydroxyl group and an amino group.
    • Synthesis: Synthesized from tryptophan in a multi-step enzymatic process.
    • Metabolism: Breakdown of 5-HT into 5-hydroxyindoleacetic acid (5-HIAA) which is excreted in the urine.
    • Dietary Sources: Found in bananas, strawberries, pineapples, tomatoes.
    • Storage: Synthesized in the CNS and enterochromaffin cells in the gut. Stored in the gut by platelets and also in the CNS.
    • Drugs: Affecting 5-HT levels: These include appetite suppressant fenfluramine, ecstasy, and carbohydrate-rich diets.
    • 5-HT Receptors: Numerous subtypes (5-HT1, 5-HT2, 5-HT3, 5-HT4, etc). These receptors have diverse functions, influencing various physiological processes.
    • 5-HT Agonists and Antagonists: Effective in various conditions (e.g., migraines, and other neurological or psychiatric disorders)

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    Explore the complex role of histamine in the body through this quiz. Test your knowledge on how histamine affects blood vessels, its influence on immune components, and its relevance to conditions like allergies and asthma. Each question delves into the physiological actions of histamine and its various receptors.

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